Although not as yet firmly established, the relatively irreversible form of transcriptional control probably represents one of the major events in cellular differentiation. In contrast, the readily reversible control is more likely to represent protein-nucleic acid and protein- protein interactions expressed as a result of postsynthetic modifications including phosphorylation, acetylation, and methylation of both the histones and the acidic chromosomal proteins. In view of the paucity of information in this area it is not as yet possible to differentiate between structural and functional proteins that are associated with DNA in the eucaryotic cell. It is the goal of this laboratory to examine these proteins and their modification in the protein nucleic acid and protein-protein interactions and their effect on transcription of RNA.